Nuclear medicine is a branch of medicine dealing with the use of radioisotopes as radiopharmaceuticals or radioactive tracers in the diagnosis and treatment of disease. Radioisotopes are natural or artificially created isotopes (isotopes being one of two or more atoms having the same atomic number but different mass numbers) of a chemical element that have an unstable nucleus that decays, emitting alpha, beta, or gamma rays until stability is reached.
Radioisotopes, such as the meta stable Technetium-99m (Tc-99m), are used in medical tests as radioactive tracers that medical equipment can detect in the body. Other generator-derived radioisotopes that are used as tracers include yttrium-90, rhenium-188, and gallium-68. Tc-99m, in particular, emits readily detectable gamma rays, and it has a half-life of 6 hours. A variety of different radiopharmaceuticals based on Tc-99m are used for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood and tumors. Schwochau, Klaus. Technetium, Wiley-VCH (2000) (ISBN 3-527-29496-1). Scientists continue to find new uses for radioisotopes, such as Tc-99m. For example, doctors recently used Tc-99m to diagnose precisely the infected lymph nodes in breast cancer patients by injecting Tc-99m into the breast around the tumor to allow them to locate the node quickly and precisely before ever making an incision. Brookhaven National Laboratory site on the history of the technetium cow. (http://www.bnl.gov/bnlweb/history/Tc-99m.asp).
A Tc-99m generator, often called a technetium cow, is a device used to extract Tc-99m from decaying molybdenum-99 (“Mo-99”). Mo-99 has a half-life of 66 hours and can be transported over long distances to radiopharmacies and hospitals where its decay product Tc-99m is used for nuclear medicine diagnostic procedures. Removing the Tc-99m from the generator (“milking” the generator) is typically done every 6 hours or, at most, twice daily. Most commercial generators use column chromatography, in which Mo-99 is adsorbed onto alumina. Normal saline solution can be run through a column of immobilized Mo-99 to elute soluble Tc-99m, resulting in a saline solution containing the Tc-99m.
Today, commercial radiopharmacies typically replace their generators on a bi-weekly basis, since the useful life of a Tc-99m generator is about 6 half lifes or approximately two weeks. Hence, typical clinical nuclear medicine units purchase at least one such generator every two weeks or order several in a staggered fashion. The lead-lined generators are heavy and bulky and represent significant manipulation and toil for personnel to replace and to dispose of spent generators. Large quantities of lead, molded plastic containers, and packing materials are used only once and discarded after two weeks. Shipping costs and waste are real considerations for end-users. Further, conventional generator systems lack flexibility as they are limited to fixed activity denominations per unit sold, resulting in limited predictability and reproducibility. Typical generators also do not provide activity above 19 Ci.
It would be desirable therefore to provide systems and methods for producing customized, predictable and reproducible supplies of radioisotopes, including high activity levels, that do not require weekly replacement, handling and transport of heavy shielding materials associated with conventional generators.